In the construction field, it is known to use metal tubular elements of a modular type that are suitably connected to each other to form a pipe that allows to transfer concrete from a container, for example a concrete mixer, to the casting zone, by means of pumping devices.
The tubular elements are connected to each other on each occasion depending on the characteristics of the zone to be reached. In particular, to allow a possible change in direction, the rectilinear tubular elements are connected to curved tubular elements which have standardized angles of longitudinal development, such as for example 15°, 30°, 45°, 60° or 90°.
The curved tubular elements, compared with the rectilinear ones, are more subject to an abrasive action mainly due to the action of the centrifugal force that the concrete exerts on their inner surface, in particular on the most external part, that is, near the extrados, depending on the conveyance speed and the radius of curvature of the tubular element itself.
In particular, near the extrados of the curved tubular element the speed at which the concrete is conveyed is much higher than the speed near the intrados, that is, in the zone with the smallest radius of curvature, and therefore the inner surface of the curved tubular element near the extrados is subject to greater wear.
In particular, the European patent application EP-A-1,873,440, in the name of the Applicant, discloses a curved tubular element that comprises a first tubular part, more external, made of material having a high mechanical resistance, and a second tubular part, disposed inside the first part and made of wear resistant material. In other words, in the known curved tubular element, there are two curved pipes, of different material, one inside the other.
In order to clamp the two tubular parts together, on the outer surface of the second tubular part, near its extrados, spacer elements are made that keep it separate from the first tubular part in order to create a casting chamber which, during the first use of the curved tubular element, is filled with concrete which, once solidified, makes the two tubular parts solid with each other. The known curved tubular element has the disadvantage, however, that it is rather complex to make, is very heavy and very expensive.
Moreover, given the curved conformation of the tubular element, it is difficult to introduce the second tubular part inside the first tubular part due to the need to force both parts.
In order to reduce the force needed for this insertion, in some known solutions, the second tubular part is made in sectors with a circumferential extension, which are inserted individually into the first tubular part and brought close to each other.
However, this known solution does not eliminate all the disadvantages and makes it difficult to produce the element; a further clamping step of the second tubular part with respect to the first is also necessary.
U.S. Pat. No. 4,199,010 describes a solution in which a metal tube for conveying material in particles is lined with a ceramic lining.
Purpose of the present invention is to achieve a curved tubular element for conveying concrete or other abrasive materials in the fluid state, which is reliable, simple to produce, relatively light and economical.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.